Determination of a constituent related property of a multi-constituent sample

A sample property monitor comprising an output unit for outputting an electromagnetic wave for interaction with a multi-constituent sample;

• a detection unit for detecting a property of the electromagnetic wave after its interaction with the multi-constituent sample and outputting the detected property of the electromagnetic wave as measurement data;
• a perturbations unit adapted to generate a perturbation in the multi-constituent sample selected to induce a change associated with a sample property to be determined, said change manifesting as a change in the property of the electromagnetic wave detected by the detection unit;
• and a determinations unit for determining the sample property from the output measurement data;
• wherein the detection unit is adapted to operate in a timed relationship with the operation of the perturbations unit to detect the property of the electromagnetic radiation a plurality of times following generation of the perturbation and to output a time-series of measurement data;
• and wherein the determinations unit is adapted to process the time-series of measurement data to determine the constituent related sample property by the application of a calibration linking the sample property to the time-series of measurement data, which calibration is empirically derived from multivariate chemometric modelling of time-series measurement data recorded for each of a plurality of reference samples following the generation of the perturbation in each sample, each reference sample having a different known value of the sample property.